1. Field of the Invention
The present invention relates to a flip-chip type group III nitride semiconductor light-emitting device having an n-electrode and a p-electrode on the same surface side and capable of outputting light from the substrate side.
2. Background of the Invention
For example, in group III nitride semiconductor light-emitting devices, even when a p-type layer is subjected to a low-resistance treatment, since the p-type layer is higher in resistivity than an n-type layer, the current does not substantially spread in a lateral direction within the p-type layer, and light emission occurs only directly under the electrode. Thus, it is necessary to form an electrode layer over a wide range on the upper surface of the p-type layer. Also, in view of the fact that an insulating material such as sapphire is used as a substrate, it is necessary to form an electrode relative to the n-type layer as a lower layer on the upper surface of the device. In order to achieve this, there was taken a measure in which the p-type layer, the light-emitting layer and so on existing in an upper portion of an n-electrode forming region are removed by means of etching, an n-pad electrode for power supply is formed on the upper surface of the exposed n-type layer, a p-electrode is then formed, and a p-pad electrode for power supply is formed in a part on the p-electrode.
However, in particular, in flip-chip type group III nitride semiconductor light-emitting devices using a transparent electrically conductive film as the p-electrode and having a reflector provided in an upper part thereof, in the case where one n-pad electrode and one p-pad electrode are provided, it is difficult to allow the current to evenly diffuse in a surface direction in the transparent electrically conductive film, leading to a problem that an even current density is not obtained on the surface of the p-type layer. It is meant by this matter that there is a problem that the light emission on surface is not even and becomes non-uniform. Then, in order that the current supplied from the p-pad electrode may evenly flow in a horizontal direction on the surface of the transparent electrically conductive film, a technology described in the following Patent Document 1 is known.
According to the technology disclosed in the following Patent Document 1, a transparent electrically conductive film is formed in a comb-toothed shape where plural strips are arranged, plural intermediate electrodes which are connected to the respective strips in plural places are provided, and these plural intermediate electrodes and some p-bump electrodes for power supply are connected to each other. According to such a configuration, the current with an even current density is allowed to flow on the surface relative to the p-type layer.
Patent Document 1: JP-A-2010-27824
However, in the case of the structure of Patent Document 1, distances between the two n-intermediate electrodes and the respective p-intermediate electrodes formed on the transparent electrically conductive film are not equal, and taking into consideration the electrode-to-electrode potential distribution, a power line with a uniform density is not always formed. Accordingly, in order to supply a current with a uniform current density to the p-layer to realize uniform light emission, there is a limit even in the structure of Patent Document 1.
Also, there is a tendency that as the transparent electrically conductive film is formed thick in an even thickness, the sheet resistance becomes lower, and the current flowing in the horizontal direction on the surface of the transparent electrically conductive film diffuses and is made uniform. However, there is involved such a problem that as the transparent electrically conductive film is formed thick, the absorption of light by the film more increases, whereby the light extraction efficiency is lowered.